Finished lubricants used for automobiles, diesel engines, axles, transmissions, and industrial applications consist of two general components, a lubricating base oil and additives. Lubricating base oil is the major constituent in these finished lubricants and contributes significantly to the properties of the finished lubricant. In general, a few lubricating base oils are used to manufacture a wide variety of finished lubricants by varying the mixtures of individual lubricating base oils and individual additives.
Numerous governing organizations, including original equipment manufacturers (OEM's), the American Petroleum Institute (API), Association des Consructeurs d' Automobiles (ACEA), the American Society of Testing and Materials (ASTM), and the Society of Automotive Engineers (SAE), among others, define the specifications for lubricating base oils and finished lubricants. Increasingly, the specifications for finished lubricants are calling for products with excellent low temperature properties, high oxidation stability, and low volatility. Currently, only a small fraction of the base oils manufactured today are able to meet these demanding specifications.
Syncrude prepared from the Fischer-Tropsch process comprise a mixture of various solid, liquid, and gaseous hydrocarbons. Those Fischer-Tropsch products which boil within the range of lubricating base oil contain a high proportion of wax which makes them ideal candidates for processing into lubricating base oil stocks. Accordingly, the hydrocarbon products recovered from the Fischer-Tropsch process have been proposed as feedstocks for preparing high quality lubricating base oils. When the Fischer-Tropsch waxes are converted into Fischer-Tropsch base oils by various processes, such as by hydroprocessing and distillation, the base oils produced fall into different narrow-cut viscosity ranges. Typically, the kinematic viscosity of the various cuts will range between 2.1 cSt and 12 cSt at 100 degrees C. Since the kinematic viscosity of lubricating base oils typically will fall within the range of from 3 to 32 cSt at 100 degrees C., the base oils that fall below 3 cSt at 100 degrees C. have limited use and, consequently, have less market value.
The Fischer-Tropsch process typically produces a syncrude mixture containing a wide range of products having varying molecular weights but with a relatively high proportion of the products characterized by a low molecular weight and viscosity. Therefore, usually only a relatively low proportion of the Fischer-Tropsch products will have viscosities above 3 cSt at 100 degrees C. which would be useful directly as lubricating base oils for the manufacture of commercial lubricants, such as engine oil. Currently, those Fischer-Tropsch derived base oils having kinematic viscosities below 3 cSt at 100 degrees C. have a limited market and are usually blended or cracked into lighter products, such as diesel and naphtha. However, diesel and naphtha have a lower market value than lubricating base oil. It would be desirable to be able to upgrade these low viscosity base oils into products suitable for use as a lubricating base oil.
Conventional base oils prepared from petroleum derived feedstocks having a kinematic viscosity below 3 cSt at 100 degrees C. have a low viscosity index (VI) and high volatility. Consequently, low viscosity conventional base oils are unsuitable for blending with higher viscosity conventional base oils because the blend will fail to meet the VI and volatility specifications for a lubricating base oil. Surprisingly, it has been found that Fischer-Tropsch derived base oils having a kinematic viscosity above 2 and below 3 cSt at 100 degrees C. have exceptionally low volatilities due to their extremely high VI's. Even more surprising was that when the low viscosity Fischer-Tropsch derived distillate fraction was blended with certain higher viscosity petroleum derived lubricating base oils, a VI premium was observed, i.e., the VI of the blend was significantly higher than would have been expected from a mere averaging of the VI's for the two fractions. In addition, due to the inherent oxidation stability of the Fischer-Tropsch derived base oils, finished lubricants prepared from blends containing them will generally require lower amounts of antioxidant additives and will be less likely to form insoluble oxidation products which result in the presence of sludge and deposits. Also due to the excellent UV stability of the Fischer-Tropsch derived base oils, the finished lubricants usually will require the addition of less UV stabilizers than needed with conventionally derived lubricating base oils. Finally, the Fischer-Tropsch derived distillate fraction is characterized by very low total sulfur which makes them excellent candidates for upgrading conventional petroleum derived base oils which typically contain between 10 and 5000 ppm total sulfur. Since the highest total sulfur usually will be found in the heaviest fractions derived from conventional oils, the present process is especially useful for upgrading heavy conventionally derived petroleum fractions. Consequently, it is has been discovered that the low viscosity Fischer-Tropsch derived base oils may be advantageously employed as blending stock with higher viscosity conventional petroleum derived base oils to prepare premium lubricating base oils and finished lubricants.
While lubricating base oil blends containing Fischer-Tropsch derived base oils have been described in the prior art, the method used to prepare the lubricating base oils and the properties of the prior art blends differ from the present invention. See, for example, U.S. Pat. Nos. 6,332,974; 6,096,940; 4,812,246; and 4,906,350. Specifically, it has not been previously taught that Fischer-Tropsch fractions having a kinematic viscosity of less than 3 cSt at 100 degrees C. can be blended with conventional petroleum derived base oils to prepare lubricating base oils suitable for blending finished lubricants meeting the specifications for SAE Grade 0W, 5W, 10W, and 15W multi-grade engine oils; SAE 70W, 75W, and 80W gear lubricants; and ISO Viscosity Grade 22, 32, and 46 industrial oils. With the present invention, this becomes possible.
When referring to conventional lubricating base oils, this disclosure is referring to conventional petroleum derived lubricating base oils produced using petroleum refining processes well documented in the literature and known to those skilled in the art.
As used in this disclosure the word “comprises” or “comprising” is intended as an open-ended transition meaning the inclusion of the named elements, but not necessarily excluding other unnamed elements. The phrase “consists essentially of” or “consisting essentially of” is intended to mean the exclusion of other elements of any essential significance to the composition. The phrase “consisting of” or “consists of” are intended as a transition meaning the exclusion of all but the recited elements with the exception of only minor traces of impurities.